1. Field of the Invention
The present invention relates to a secondary battery provided with a safety valve device.
2. Description of Related Art
In some secondary batteries, a battery case for storing a power generating element is provided with a safety valve (a safety valve device) having an excessive pressure preventing function. Such the safety valve device is provided for preventing an excessive increase of inner pressure in the battery case and preventing a breakage of the battery case by opening the safety valve to safely release gas out of the battery case when the inner pressure in the battery case rises, more specifically, when the inner pressure extremely rises due to a mass amount of gas generated from the power generating element.
Among such secondary batteries, for example, in a nickel-metal hydride secondary battery, inner pressure in a battery case could be increased depending on electric charge and discharge cycle even if the battery performance does not largely decline. In response to this, such the secondary battery is provided with a restorable safety valve device as a safety valve (a safety valve device) that is able to reseal a valve after once opening the valve.
Further, concerning the above mentioned nickel-metal hydride secondary battery, it is disclosed that a safety valve device having a hydrogen leaking function to control fluctuations of discharge reserve and charge reserve in a negative electrode in addition to the excessive pressure preventing function (see FIG. 2 of WO2006/004143).
However, the restorable safety valve device disclosed in FIG. 2 of WO2006/004143 requires a spring member and a holding member besides a valve member, resulting in a complicated structure.